This invention relates to a tire forming drum suitable for use in so-called single stage forming wherein a green tire is completely produced on one forming drum. More particularly it relates to a tire forming drum capable of sufficiently preventing residual air in tire bead portions.
A conventional tire forming drum of this kind generally includes a pair of bead lock means, shaping means and ply turning-up means for turning up a ply of a tire. In forming a tire with this forming drum, as shown in FIG. 1 bead cores b are arranged on the outer side of an inner lining (a) such as an inner liner or a carcass ply. With the bead cores b supported together with the inner lining (a) by increasing diameters of bead lock means c, pressurized air is injected into inside of the inner lining (a) by means of the shaping means (not shown). At the same time, a crown portion of the inner lining (a) is joined with the inner circumferential surface of a belt-tread band d by movement of the pair of bead lock means toward each other, while the configuration of the tire is conditioned. Thereafter, both side edges of the inner lining (a) are folded thereupon or turned up as shown in FIG. 1 by means of ply turning-up means (not shown). Moreover, stitcher rolls e are urged against the tire so that the air existing between the laminated layers of the tire is expelled therefrom and the layers are sufficiently joined with each other.
With such a forming drum of the prior art, however, the urging force of the stitcher rolls e applied to the tire is supported only by the shaping inner pressure jetted into the inner lining (a). Therefore, bead portions of the tire are likely to be deformed due to insufficient support of the urging force of the stitcher rolls e. Consequently, it is impossible to pressurize the inside of the bead portions to a required pressure of this. As a result of this, the air is permitted to remain between the bead portions and the carcass ply as shown by hatched portions in FIG. 1.
In order to solve this problem, it has been proposed that shoulder bladders f are used to urge inner circumferential surfaces of bead portions toward stitcher rolls as shown in FIG. 2. However, the shoulder bladders f could not still sufficiently support the urging force of the stitcher rolls e. Moreover, owing to the existence of the bead lock means c the shoulder bladders f could not be brought into sufficiently close contact with the bead portions, particularly, the radially inner ends thereof. Accordingly, a high stitching effect could not be substantially accomplished in this prior proposal.